1. Field of the Invention
This invention relates to a styrene resin having excellent moldability or formability and physical properties and a composition of said styrene resin and a thermoplastic polycarbonate resin. More specifically, the present invention pertains to a styrene resin which has excellent moldability or formability, does not undergo heat deterioration easily and has improved heat resistance and impact resistance; and a composition of said styrene resin and a thermoplastic polycarbonate resin.
2. Description of the Related Art
A styrene resin is conventionally known as a resin having excellent heat resistance and impact resistance and is used as a molding or forming material. For example, it is used for automobile parts, household electric parts, office machinery parts, mechanical parts or the like. In recent years, it has come to be used frequently as a material for large-sized thin-wall formation or high-speed injection molding, but the conventional resin is not satisfactory for such an application, due to low fluidity upon processing, its moldability or formability is poor and much time is required for processing. In addition, as the range of a molded or formed product widens with a decrease in the wall thickness of the product, the resin is required to have good impact resistance.
From a mixture of the styrene resin and a thermoplastic polycarbonate resin which is added in order to heighten the impact resistance of the styrene resin, a molded product having high impact resistance is available. Such a resin composition needs a higher molding or forming temperature to heighten its fluidity, but an increase in the molding or forming temperature causes a deterioration in its physical properties due to thermal decomposition of the rubber phase in the styrene resin.
On the other hand, recycling of such a general-purpose plastic material is desired from the viewpoint of maintaining the environment on the earth so that a recycling method is under investigation. In this case, deterioration of its physical properties due to thermal decomposition of a rubber phase in the styrene resin occurs when the plastic material is molded or formed in repetition.
Particularly when a thermoplastic polycarbonate resin is used as an impact strength improving agent, emulsion polymerization is frequently employed for preparing a styrene resin which is ordinarily known as an ABS resin. This process is however accompanied with the problem that an emulsifier or coagulant used for the preparation of the styrene resin remains in the resin and such impurities in the ABS resin cause deterioration of the resin and lower its physical properties or thermally change the color of the resin, which prevents the resin from recycling use.
For example, in Japanese Patent Application Laid-Open No. 240352/1987 from line 12 of the left column on page 1 to line 20 of the upper right column on page 2, disclosed is a process which comprises mixing an aromatic thermoplastic polycarbonate resin with a graft copolymer which has been obtained by the graft copolymerization of at least two monomers selected from aromatic vinyl monomers, vinyl cyanide monomers and alkyl methacrylate ester monomers on a rubbery polymer, contains at least 60 wt. % of a rubbery polymer component, has a graft ratio of less than 50% to the rubbery polymer and has a non-graft resin component of an intrinsic viscosity of 0.6 dl/g or lower.
In the above-described process, owing to a large content of the rubbery polymer in the polymer, mechanical strength, particularly, stiffness lowers largely and in addition, fluidity lowers. In addition, heat resistance must be improved. Moreover, emulsion polymerization, which is adopted as a polymerization method, needs subsidiary raw materials such as an emulsifier and also waste water treatment, which makes the process complex and cost-consuming. Thus, the problems of the above-described process have remained yet.
In Japanese Patent Publication No. 39176/1987, from line 39 on the left column to line 42 on the right column on page 2, disclosed is a process which comprises mixing, with a thermoplastic polycarbonate resin and two ABS resins, each ABS resins having a rubber particle size and graft ratio within a specific range, but being different from each other, thereby the impact resistance at low temperatures is improved.
The above-described process is however complex and therefore industrially disadvantageous, because two graft polymers having different compositions are prepared respectively, a copolymer is prepared from another monomer mixture and then, the resulting graft polymers are mixed with a thermoplastic polycarbonate resin.
In Japanese Patent Application Laid-Open No. 148258/1986, from line 10 on the right column on page 1 to line 15 on the lower right column on page 2, disclosed is a process in which two ABS resins having a low rubber content and a high rubber content, respectively and, if necessary, an AS resin are mixed in order to improve the balance between heat resistance, impact resistance and moldability or formability.
It is however difficult to prepare an ABS resin having a high rubber content and high graft ratio without a limitation on the preparing process and particularly, bulk polymerization cannot be applied. In addition, this process is also complex because, similar to the above-described case, two or three ABS resins and, if necessary, one AS resin must be prepared respectively and they are mixed with a thermoplastic polycarbonate resin.
The conventional styrene resin, such as ABS resin, containing a rubbery polymer is prepared by emulsion polymerization, bulk polymerization or solution polymerization, but, some styrene resins happen to undergo denaturation and are colored seriously by heating.
When a styrene resin is formed into a corresponding alloy with a thermoplastic polycarbonate resin, it happens to have lowered mechanical physical properties owing to the hydrolysis of the thermoplastic polycarbonate resin, which however depends on the kind of the styrene resin.
There is accordingly a demand for the provision of a styrene resin composition which can be molded or formed at a relatively low temperature, is not deteriorated or colored even by the molding or forming at high temperature or molding or forming in repetition, and has largely improved moldability or formability, good heat resistance and improved impact strength.
An object of the present invention is to provide a resin composition of a styrene resin, which is excellent in moldability or formability and physical properties, with a thermoplastic polycarbonate resin. There is a strong desire for the development of a process which can provide, at a low cost, a resin composition of a styrene resin and a thermoplastic polycarbonate resin, said styrene resin causing no deterioration of the thermoplastic polycarbonate resin after mixing and having largely improved moldability or formability, good heat resistance and improved impact resistance.
With a view to overcoming the above-described defects, the present inventors have carried out various investigations. As a result, it has been found that an amount of a specific component contained in a styrene resin has an influence on the deterioration of the physical properties of the styrene resin, leading to the completion of the present invention.
Described specifically, the present invention has the following constitution:
(a) A styrene resin which comprises 50 to 90 wt. % of a continuous phase component (S) composed of a copolymer of a styrene monomer and an unsaturated nitrile monomer, or a styrene monomer, an unsaturated nitrile monomer and another monomer copolymerizable therewith; and 10 to 50 wt. % of a dispersed phase component (which will hereinafter be called xe2x80x9crubbery polymer componentxe2x80x9d) composed of a rubbery polymer component on which said monomers have been grafted and which has occluded said copolymer; wherein a triple consecutive chain unit AAA cannot be detected from the unsaturated nitrile monomer units (A) in the continuous phase component (S) and a double chain consecutive unit AA amounts to 3% or less based on the whole units (A) detected, a reduced viscosity (xcex7sp/c) of the continuous phase component (S) is 0.2 to 0.85 dl/g and an amount of metal component of Group I and/or II of the periodic table is less than 100 wt.ppm or less in terms of a metal.